1. Field of the Invention
The present invention relates to a drive method for a liquid crystal display device and a drive circuit and, more particularly, to a drive method and a drive circuit applied to a liquid crystal device of a double scanning line system having a color filter having a lateral stripe arrangement.
2. Description of the Related Art
In the field of a liquid crystal display device, there is a demand to reduce the cost by reducing the number of expensive data drivers. A TFT substrate having the following structure, is proposed. That is, thin film transistors (to be referred to as TFTs hereinafter) of pixels sandwiching one data line (signal line) are arranged on both the sides of the data line, and these TFTs are driven by different gate lines (scanning lines), respectively. In this structure, since two gate lines are required for one row of pixels arranged along a gate line, although the number of gate lines are twice the number of gate lines of a conventional structure, two rows of pixels laterally arranged on both the side of the data line are driven by one data line arranged between these pixels. For this reason, the number of data lines is half of the number of data lines of the conventional structure. As a result, the number of data drivers can be reduced. In this specification, a drive method for a substrate of this type is called a double scanning line system.
A color filter halving various array patterns is combined to the TFT substrate of the double scanning line system, so that a color liquid crystal display device can be realized. As a drive method for the liquid crystal display device, dot inversion driving which can achieve a high-quality display with high contrast, low crosstalk, and the like as a characteristic feature may be used.
When a liquid crystal display device is to be driven, gate lines are sequentially scanned to turn TFTs on, and a drive voltage is written on liquid crystal capacitors constituted by pixel electrodes, common electrodes, and liquid crystal layers of pixels through data lines. Thereafter, although the written drive voltage is kept after the TFTs are turned off, charges accumulated in the liquid crystal capacitors partially leak through the TFTs with time.
In this case, when the dot inversion driving is employed, dots on which a voltage having a positive polarity is written and dots on which a voltage having a negative polarity is written are regularly arranged in a display area. However, a leakage current characteristic in an OFF state of the TFTs in a positive state is different from that in a negative state. For this reason, a variation in transmittance ratio of a liquid crystal with time in a dot on which a positive voltage is written is made different from that in a dot on which a negative voltage is written.
In a color filter using three colors, i.e., red (R), green (G), and blue (B) as basic colors, the ratio of the transmittance ratios of the respective colors is given by R:G:B=32:55:13. For this reason, a user of a liquid crystal display device visually recognizes a variation in transmittance ratio of a green dot more dominantly.
FIG. 14A shows a pattern so-called lateral stripes in which the same basic colors of the color arrays of the color filter are laterally arrayed, and shows the drive voltage polarities of dots in one arbitrary field. In this manner, when the dot inversion driving is used when the color filter has lateral stripes, G dots (in FIG. 14A, dots enclosed by oval circles) on which a positive voltage is written and G dots (in FIG. 14A, dots enclosed by rectangles) on which a negative voltage is written are laterally arrayed. As shown in FIG. 14B, in a transmittance ratio distribution, wave crests and wave troughs are repeated at a cycle B (in FIG. 14B, crests are indicated by a solid line, and troughs are indicated by a broken line).
Therefore, while the user""s eyes pass through the plurality of fields, a so-called line crawling phenomenon in which the crests and troughs of the transmittance ratio distribution are visually recognized such that the crests and troughs flow linearly flow on a screen is generated, and display quality is disadvantageously degraded.
The present invention has been made to solve the above problem, and has as its object to provide a drive method and a drive circuit for a liquid crystal display device in which a line crawling phenomenon is not visually recognized even if inversion driving is applied to a liquid crystal display device of a double scanning line system having a lateral-stripe color filter.
In order to achieve the above object, a drive method for a liquid crystal display device according to the present invention is characterized by comprising the steps of: arranging a plurality of data lines and a plurality of gate lines on a substrate in the form of a matrix; arranging pixel electrodes controlled by signals of the data lines on both the sides of each data line such that the pixel electrodes correspond to the plurality of gate lines; arranging the plurality of gate lines such that the pixel electrodes on both the sides of the data lines are controlled by signals of gate lines arranged to sandwich these pixel electrodes; controlling adjacent pixel electrodes between adjacent data lines by a signal of one gate line of the gate lines arranged to sandwich the pixel electrodes; controlling adjacent pixel electrodes between adjacent data lines which are adjacent to, through a data line, the adjacent pixel electrodes between the adjacent data lines and adjacent pixel electrodes between adjacent data lines which are adjacent to, through a gate line, the adjacent pixel electrodes between the adjacent data lines controlled by one gate line by a signal of the other gate line of the gate lines arranged to sandwich the pixel electrodes; repeatedly arraying combinations of a plurality of basic colors in the same order with respect to the pixel electrodes arranged along the gate line directions; and, by using a liquid crystal display device having a color filter in which the same basic colors are arranged for the pixel electrodes arranged along the data line directions as an object, performing polarity inversion of every multiple-of-two pixel electrodes in a direction along the data line and adding liquid crystal drive voltages subjected to polarity inversion every multiple-of-two pixel electrodes controlled by the same data line in the direction along the gate line.
The present invention is applied to a liquid crystal display device of a double scanning line system having a lateral-stripe color filter. In addition, even in double scanning line systems, the present invention is applied to a liquid crystal display device having a TFT substrate having a design layout in which, in particular, as described above, two adjacent pixel electrodes between adjacent data lines are controlled by one gate line of two gate lines sandwiching the pixel electrodes, and two adjacent pixel electrodes which are adjacent to the two pixel electrode through the data line and two pixel electrodes which are adjacent to each other through the gate line are controlled by the other gate line.
As in the prior art, when conventional dot inversion driving is applied to a liquid crystal display device of a double scanning line system having a lateral-stripe color filter, a line crawling phenomenon caused by the crests and troughs of a transmittance ratio distribution is generated.
In contrast to this, according to the present invention, simple dot inversion driving is not performed to the liquid crystal display device using the double scanning line system having the above design layout, but the following driving is performed to the liquid crystal display device, so that visual recognition of the line crawling phenomenon can be suppressed. That is, polarity inversion of every multiple-of-two pixel electrodes such as every two pixel electrodes, every four pixel electrodes, . . . , in a direction along a data line, and polarity inversion of every two pixel electrodes connected to the same data line in a direction along a gate line.
Polarity inversion inherent in the present invention is performed, so that the following two effects are achieved.
(1) The cycle of a transmittance ratio distribution can be shortened (interval between crests). In other words, the spatial frequency of a variation in transmittance ratio can be made high.
(2) The present invention can give periodicity to a transmittance ratio distribution such that portions corresponding to the crests and troughs of the transmittance ratio distribution do not uniformly continue in a longitudinal direction, but the crests and troughs alternately appear.
With respect to (1), since the visibility of a variation in transmittance ratio has a characteristic that the variation in transmittance ratio is easily checked as the spatial frequency becomes low, the variation in transmittance ratio is not easily checked as the spatial frequency becomes high. With respect to (2), when portions corresponding to the crests and troughs continue to have large lengths, the portions are easily recognized as one line, and the portions are not easily visually recognized such that the crests and troughs are alternately intermittent. In this manner, according to the drive method of the present invention, visual recognition of a line crawling phenomenon can be suppressed by the two effects. The effects will be described below with concrete examples in the embodiments of the present invention.
As the arrangement of a drive circuit for realizing the drive method, an arrangement having the following components can be used. That is, the arrangement has a gate driver for sequentially outputting gate voltages to one gate line and the other gate line of the plurality of gate lines in two fields, respectively, a data driver for outputting liquid crystal drive voltages of pixel electrodes corresponding to the gate lines to which the gate voltage is output, and a control circuit for inverting the polarities of the liquid crystal drive voltages output from the data driver to the plurality of data lines every multiple-of-two pixel electrodes in a direction along the data line, generating a polarity control signal for performing polarity inversion of every two pixel electrodes controlled by the same data line in a direction along the gate line, and outputting the polarity control signal to the data driver.
More specifically, the gate driver can be constituted by a circuit having two sets of shift registers and level shifters for outputting gate voltages to two series of gate lines called one gate line and the other gate line as described above. As the data driver, a generally available data driver can be used. Image data of basic colors such as R, G, and B are generally assigned to three data buses. In the present invention, since the number of data lines in the liquid crystal display device of the present invention is half of the number of data lines in the conventional liquid crystal display device, interpolation and replacement of data are performed, and the data on the data buses do not correspond to the image data of the basic colors.
The control circuit can be generally constituted by an ASIC such as a gate array or the like. The control circuit may be constituted by an arrangement having a circuit portion constituted by a latch, a multiplexer, and the like for supplying an image signal to the data driver and a circuit portion constituted by a horizontal counter, a vertical counter, a pulse decoder, and the like for generating a polarity control signal for regularly inverting the polarity of the liquid crystal drive voltage as described above.
In the liquid crystal display device to which the present invention is applied, advantages such as cost reduction and low power consumption can be achieved. For this reason, the present invention is suitable for the field of the liquid crystal display device such as a portable terminal which is particularly desired to be reduced in weight and size. Therefore, the present invention is suitably applied to the liquid crystal display device in which the diagonal size of a screen is about 3 to 10 inches, and a dot pitch is about 30 to 300 pm (depending on a pixel capacity).